Chemistry Chapter 12 Test
what are the steps needed to solve a mass-mass stoichiometry problem?
1. mass-mole conversion 2. mole ratio from balanced equation 3. mole-mass conversions
4 factor that cause percent yields to be less than 100%
1. reactions do not always go to completion 2. impure reactants 3. actual yield could be lower that theoretical 4. reactants and products are not carefully measured
what is the first step for determining the amount of products?
convert each quantity of reactants to moles
the amount of a substance is usually determined by measuring its mass in _______
grams
what is ALWAYS conserve in every equation?
mass and atoms
What quantities are conserved in every chemical reaction?
mass and volume are conserved in every chemical reaction
What is the general procedure for solving a stoichiometric problems?
the given quantity is first converted to moles, then the mole ratio from the balanced equation is used to calculate the number of moles the wanted substance. Finally the moles are converted to any other unit of measurement related to the unit mole, as the problem requires
What does the percent yield of a reaction measure?
the percent yield is a measure of the efficiency of a reaction carried out in the laboratory
In terms of what quantities can you interpret a balanced equation?
a balanced equation can be interpreted in terms of different quantities, including numbers of atom, molecules, or mole; mass; and volume
quantity usually means the ________ of a substance expressed in grams or moles
amount
what is essential for all calculation involving amounts of reactants and products?
balanced chemical equation
How is a balanced equation like a recipe?
balanced equations provide the same kind of quantitive information that a recipe does
stoichiometry
calculation of quantities in chemical reactions is a subject of chemistry
How do chemists used balanced equation?
chemist use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction
mole ratio
conversion factor derived from the coefficients of a balanced chemical equation interpreted in terms of moles
true/false: laboratory balances are used to measure moles of substances directly
false: no lab balance can measure substance directly in moles
true/false: the actual yield is greater than the theoretical yield
false: smaller
true/false: chemical reaction stops before the limiting reagent is used up
false: the chemical reaction does not stop until the reagent is used
true/false: If you know the number of moles of one substance in a reaction you need more information than the balanced chemical equation to determine the number of mole of all the other substance in the reaction
false: you get information from the equation
how can you determine the quantities of reactants and products in a chemical equation?
from a balanced equation
How is the amount of produce in a reaction affected by an insufficient quantity of any of the reactants?
in a chemical reaction an insufficient quantity of any of the reactants will limit the amount of product that forms
How are mole ratios used in chemical calculations?
in chemical calculation, mole ratios are used to convert between moles of reactant and moles of product, between mole of reactant, or between moles of products
3 types of problems that can be solved with stoichiometric calculations
mass-volume volume-volume particle-mass
theoretical yield
maximum amount of proud that could be formed from given amounts of reactants
the coefficients from a balanced chemical equation are used to write conversion factors called _______________
mole ratios
in any stoichiometric calculations, the given quantity is first converted to ________
moles
percent yield
ratio of the actual yield to the theoretical yield expressed a percent Equation: Actual/theoretical x 100
the coefficients of a balanced chemical equation tell you the relative number of moles of ____________ and ____________ in a chemical reaction
reactants; products
limiting reagent
reagent that determines the amount of product that can be formed by a reaction; the reaction occur only until the limiting reagent is used up
What kind of information can you NOT get from a chemical equation?
size of particles
calculations using balanced equation are called ___________
stoichiometric calculations
actual yield
the amount of product that actually forms when the reaction is carried out in the laboratory
excess reagent
the reagent that is not completely used up in the reaction
true/false: a balanced chemical equation must obey the law of conservation of mass
true
true/false: if a sample is measured in grams, molar mass can be used to convert the mass to moles
true
true/false: stoichiometric calculation can be expanded to include any unit of measurement that is related to the mole
true
true/false: stoichiometry is the calculation in chemical reactions
true
